In a known embodiment, sealed cells have an electrochemical group including at least one alternation of negative electrode, separator, and positive electrode, together with an enclosure made up of a cover, an end wall, and a case, said case surrounding said group, and said cover and said end wall each having a respective current outlet terminal.
Cells that operate with an organic electrolyte need to be housed in an enclosure that provides adequate sealing. The case must prevent external elements such as moisture or oxygen in the air, and in particular moisture, from penetrating into the inside of the cell and thus coming into contact with the electrochemical group. In addition, said enclosure must prevent electrolyte passing out from the cell. In order to avoid making the cell pointlessly heavy, the mass of the components constituting the enclosure must be as small as possible. For high-capacity cells, in order to avoid taking up too much volume compared with the working volume of the electrochemical group, the thickness of each of the components of the enclosure must be as small as possible. In order to be technically feasible, enclosures made of metal must be of considerable thickness, e.g. 0.3 mm to 1 mm, and therefore of considerable weight. Enclosures made of plastics are lighter in weight but give rise to problems of sealing, in particular to-ingress of moisture into the cell. This requires them to be thicker, e.g. at least 1 cm thick.
Japanese application JP-A-63.181.272 describes a sealed cell comprising a one-piece enclosure constituted by an outer film of light metal, e.g. aluminum, and an inner film of resin, e.g. polyethylene, with the hermetic seals for the electrodes being provided by epoxy resin. Such cells nevertheless suffer from a problem of insufficient mechanical strength.
Thus the problem which is posed is that of providing a cell which is simultaneously sealed, both from the inside of the cell to the outside and from the outside of the cell to the inside, that possesses sufficient mechanical strength to provide said cell with a good lifetime, and whose enclosure is relatively lightweight and relatively thin. The cell of the invention solves the problem posed in that by combining two means, namely a case of multilayer material and a central supporting core, it makes it possible to provide sealing, mechanical strength, small volume occupied by the enclosure, and an overall assembly that is light in weight.